As an alternative to conventional shaft and strip mining techniques to recover ores containing valuable metals such as uranium and other elements, a technique known as leaching has recently evolved for tapping underground ore bodies, in situ, by treating the underground ore with a leaching solution (lixiviant) which establishes oxidation-reduction reactions for separating and recovering a particular element or mineral from unwanted material in the ore body. The process involves mainly drilling an injection well into an underground ore deposit, and then introducing the leach solution to contact the ore. The leach solution dissolves the mineral within the ore deposit, and thereafter, the pregnant solution is recovered at a recovery well and processed by conventional extraction means to recover desired minerals therefrom.
In order to avoid contaminating an underground region outside of a desired leaching zone, it has been necessary to periodically monitor water samples withdrawn from monitor wells surrounding the leaching site. The water samples are analyzed for ions contained in the water samples. An increase in ion concentration in the samples is considered to be an indication of escaping leach solution in proximity to the monitor wells which are outside the desired leaching zone.
The above method is tedious and requires manual attention by personnel. Even more important, however, it is impossible to determine the presence of escaping leach solution until the solution actually reaches the monitor wells. Detection may therefore be delayed for a substantial period of time after escape begins. Even then, false indications of escaping leach solution sometimes occur because of locally high concentrations of ions in migrating ground water. A need exists, therefore, for a method of detecting escaping leach solution to avoid contamination of regions such as farm land outside the desired leaching zone that is faster and more reliable than previously known methods.
Accordingly, one object of the present invention is to provide a new and improved method of detecting leach solution escaping from a leaching zone.
Another object is to provide a method of and apparatus for detecting escaping leach solution that does not require sampling of solutions from individual monitor wells surrounding the leaching site.
Another object is to provide a new and improved method of and apparatus for detecting escaping leach solution that is faster and more reliable than prior methods.
Another object is to provide a new and improved method of detecting escaping leach solution that is adaptable to automation to reduce personnel requirements.